The present invention pertains to a method for operating an electromechanical brake system of a motor vehicle that contains the following components:
brake actuators, one assigned to each wheel of the motor vehicle, PA1 a control unit for controlling or regulating the brake system, and PA1 two brake circuits that operate independently of one another and are supplied with power by an on-board network of the motor vehicle in the normal mode. PA1 monitoring the voltage of the on-board network in a control unit, wherein the electromechanical brake system operates in the normal mode if the voltage of the on-board network exceeds a predetermined value, and wherein the brake system operates in the emergency mode if the voltage of the on-board network voltage falls below a predetermined value, and following the features listed below: PA1 brake actuators one assigned to each wheel of the motor vehicle, PA1 a control unit for controlling or regulating the brake system, and PA1 two brake circuits that operate independently of one another and are supplied with power by an on-board network of the motor vehicle in the normal mode, wherein PA1 one emergency power storage mechanism, which supplies the respective brake circuits with power in the emergency mode, is assigned to each brake circuit, and PA1 a differentiation between the normal mode and the emergency mode can be made in the control unit, and PA1 both brake circuits are operated by the control unit in the normnal mode of the brake system, and PA1 in the emergency mode of the brake system, only one of the two brake circuits is operated by the control unit until the emergency power storage mechanism assigned to this brake circuit has reached a residual power value that is sufficient for locking the wheels of this brake circuit while the motor vehicle is at a standstill.
Brake systems of the Brake-By-Wire type were recently developed for motor vehicles, in particular, for passenger cars. In brake systems of this type, the driver decelerates the motor vehicle by exerting a force upon the brake pedal with the foot, wherein the effect of this force exerted upon the pedal is detected by a sensor and converted into an electric signal. The signal is forwarded to individual brake actuators that are assigned to each wheel of the motor vehicle and each brake actuator exerts a braking force upon the wheel of the motor vehicle, among other things with the aid of an electric motor. In contrast to conventional brake systems, the brake actuating power required for a braking maneuver is not made available in mechanical form, but rather in electrical form. Consequently, electric brake power storage mechanisms need to be provided that can supply the brake system with the required electric power during a braking maneuver. In the normal mode, an electromechanical brake system is usually powered by the on-board network of the motor vehicle.
It is no longer possible to power the brake system via the on-board network if this on-board network becomes defective or fails. For these cases, according to one legal requirement, it must also be possible to bring the motor vehicle to a standstill reliably after a certain number of brake actuations. In addition, it should also be possible to park the motor vehicle reliably, i.e., to secure the motor vehicle by actuating a parking brake that acts upon the brakes of the brake system.
An electromechanical brake system of the initially mentioned type that is supplied with electric power by the on-board network in the normal mode of the motor vehicle is known from DE 34 10 006 A1. The brake system described in this publication contains another brake circuit that is either provided in the form of a hydraulic or a mechanical brake circuit and functionally connected to the brake pedal of the brake system in addition to an electric brake circuit. Preferably, the additional brake circuit acts exclusively upon the wheels of the front axle of the motor vehicle. The mechanical brake system that is embodied with the aid of bowden cables may also be connected functionally to a manually actuated parking brake lever. If a malfunction occurs in the brake system or if there is a failure in the on-board network that leads to a failure of the electric circuit of the brake system, the brake pedal can be actuated beyond a pressure point such that the vehicle is decelerated with the aid of the hydraulic brake circuit or the mechanical brake circuit. A reliable deceleration of the motor vehicle consequently is also possible if the on-board network malfunctions or fails. In addition, the safe parking of the motor vehicle can be realized if the second brake circuit of the brake system is provided in the form of a mechanical brake circuit. In this case, the wheels of the front axle of the motor vehicle can be locked by actuating the parking brake lever while the motor vehicle is at a standstill.
The previous explanations indicate that the brake system known from DE 34 10 006 A1 fulfills the initially mentioned requirements. However, this electromechanical brake system has a complicated design because it contains a hydraulic or mechanical brake circuit in addition to an electric brake circuit. Consequently, this brake system is not able to obtain the objective of the invention, namely the creation of a reliable and exclusively electromechanical brake system (i.e., a brake system that does not contain an additional hydraulic or exclusively mechanical brake circuit).
It is accordingly an object of the present invention to be able to operate an exclusively electromechanical brake system that makes it possible to reliably decelerate and safely park a motor vehicle even if the on-board network malfunctions or fails.
A further object of the invention is to have a mechanical brake system for carrying out the aforementioned method.